Radiations of various forms such as X-Rays, gamma-Rays, UV-Rays, laser light, microwaves, electron beams as well as particle beams of, for example neutrons, and protons, have been used to treat cancer related issues. Some of said radiations have been used in such applications, in combination with radiation sensitive molecules. Electromagnetic and ionizing radiations are indeed capable in particular of breaking the DNA molecule of the cell, thereby killing cells and/or preventing said cell from growing and dividing. This effect is mainly due to indirect damages created in particular by electrons and/or high energy photons emitted after ionization that will be responsible for free radicals generation.
The term “Ionizing radiations” refers to highly-energetic particles or waves that can ionize an atom or molecule. Ionizing ability depends on the energy of individual particles or waves, and not on their number. A large flood of particles or waves will not, in the most-common situations, cause ionization if the individual particles or waves are insufficiently energetic. A typical ionizing radiation is a radiation, the energy of which is higher than 2 KeV.
Radiosensitization by gold nanoparticles (GNPs) has been identified as a promising approach for improving radiotherapy.
U.S. Pat. No. 6,955,639 (Hainfeld et al.) describes a method of enhancing X-Rays radiation effects using metal, in particular gold, nanoparticles, the size (diameter) of the metal core being preferably, for biodistribution reasons, in the range of 0.8 to 20 nm, more preferably 0.8 to 3 nm.
Herold et al. (Int. J. Rad. Biol. 76 (2000) 1357) indicate that gold nanoparticles of small size (˜2 nm) should diffuse more homogeneously throughout the tumor mass.
Chithrani et al. (Nano Lett. 6 (2006) 662; Nano Lett. 7 (2007) 1542) showed a preferential penetration and accumulation of 50-nm diameter GNPs in Hela cells.
Chang et al. (Cancer Sci. 99 (2008) 1479) showed that, in a melanoma tumour-bearing mice model, 13-nm diameter GNPs in conjunction with a single dose of 25 Gy from a 6 MeV electron beam led to a more pronounced reduction of the tumor volume than in the control groups.
Zhang et al. (Biomed Microdevices (2009), 11:925-933) provides in silico datas (Monte Carlo simulation model) confirming that gold nanoparticles can enhance the effective dose of radiation, but does not study the nanoparticle's size impact on such dose enhancement. This document refers to the 1.9 nm diameter-nanoparticles of Hainfeld in the context of radiation therapy (see page 930, right column), but provides no result which may be of help to accurately quantify a dose enhancement factor in a biological system (see Montenegro et al., J. Phys. Chem. A. 2009, 113, 12364-12369: “Monte Carlo Simulations and Atomic Calculations for Auger Processes in Biomedical Nanotheranostics”), in particular in a human being.
Inventors herein provide powerful nanoparticles, which are surprisingly able to achieve a more efficient perturbation, alteration or destruction of target cells in vitro, ex vivo and in vivo when said nanoparticles are exposed to ionizing radiations, than nanoparticles described in the prior art, as herein demonstrated.
The inventive nanoparticle is a metallic nanoparticle having advantageously, as the largest size, a size comprised between about 80 nm and about 105 nm, the nanoparticle being made of a metal having preferably an atomic number (Z) of at least 25. The advantageous properties of the herein described nanoparticles could not be extrapolated from the art which, in contradiction with the present invention, suggests the use of gold nanoparticles of small size to increase the dose enhancement factor [see in particular Brun et al. (Colloids and Surfaces B: interfaces, 72 (2009) 128-134: “Parameters governing gold nanoparticle X-ray radiosensitization”) who reveal the influence of the gold nanoparticles concentration]. The results appearing on FIG. 4(B) of Brun et al. in particular, reveal a dose enhancement factor increase when the size of gold nanoparticle decreases, for a given gold concentration (the gold content varying with the gold nanoparticle radius according to a factor 3).
For a given metal concentration and a given ionizing radiation absorption ability, the metallic nanoparticles herein described, the size of a typical metallic nanoparticle being preferably between about 80 nm and about 105 nm, are responsible for an increased therapeutic efficacy (ability to generate target cells damages) when compared to nanoparticles of smaller sizes, in particular when compared to nanoparticles having a size of 60 nm or less.
For a given metal concentration and an equivalent X-Rays attenuation at cellular level, the metallic nanoparticles herein described exhibit a stronger ability to kill cells and/or prevent their division.
Another feature exhibited by the herein described nanoparticles, is their ability, when exposed to ionizing radiations, to generate a therapeutic effect when in contact with target cells. In other words, the therapeutic efficiency observed under irradiation does not require the nanoparticles cell uptake. Such a property is herein described for the first time.
Indeed, until now, the target cell uptake was believed, in the art, to be required for the nanoparticles to be able to generate efficient cellular lethal damages under irradiation (see for example Kong et al. (Small 4 (2008) 1537)).
The present invention thus goes against the prejudice of the all prior art leading the skilled person, mainly for biocompatibility, biodistribution, and cell uptake reasons, to the use, in terms of medical applications, of nanoparticles with a diameter from about 1 to 20 nm, at most 60 nm, with a particular and long-lasting interest for 50-nm nanoparticles (see for example Chithrani et al. (2006) and Chang et al. (2008)).
The nanoparticles of the present invention further advantageously allow a reduction in the amount of metal to be administered to a subject, as well as a reduction in the number of nanoparticles administration steps, to a minimum, in the context of a complete radiotherapeutic treatment protocol, thereby favouring their tolerance by the subject.